A large number of abdominal surgical procedures are performed with laparoscopic techniques in order to avoid a large skin incision. Typically in laparoscopic surgery, a special needle (e.g. a needle similar to the needles described in U.S. Pat. No. 4,808,168 and U.S. patent application No. 07/808,152) is inserted through the skin, and used to pressurize the abdominal cavity with an insufflating gas such as carbon dioxide (CO.sub.2).
Once the abdomen is adequately dilated, the needle is removed and a rigid access tube or cannula with a diameter larger than the pneumoneedle (for example 5, 10 or 11 mm) is passed through the skin in generally the same location. To drive the cannula through the skin, the surgeon places a trocar in the lumen of the cannula to provide a sharp, leading edge for cutting tissue. The art is replete with trocar and cannula assemblies, including those shown in U.S. Pat. Nos. 4,535,773, 4,601,710, 4,654,030, 4,902,280, 4,931,042, 5,104,382, 5,116,353 and 5,152,754 the entire contents of which are herein expressly incorporated by reference.
The cannula provides access for laparoscopic surgical tools or instruments such as a tissue tacker, a stapler or a surgical clip applier. Such instruments include mechanical tissue engagement devices such as tissue tackers, staples and clips. Examples of such surgical instruments are described in U.S. Pat. Nos. 5,040,715, 5,084,057, 5,100,420, 5,171,247, 5,171,247, 5,174,487 and 5,176,695 (the entire contents of each of which are herein expressly incorporated by reference).
It may be difficult to determine whether the supply of tissue engagement devices in an existing surgical instrument is depleted (e.g. whether the instrument is spent), particularly during a laparoscopic surgical procedure where a surgeon's attention may be focused elsewhere. U.S. Pat. Nos. 5,084,057 and 5,171,247 disclose laparoscopic clip appliers which have devices which address this problem. However, valuable time during the laparoscopic surgical procedure may be wasted by inserting a spent surgical instrument through the cannula.
A surgical instrument such as a laparoscopic surgical stapler has jaws for clamping on tissue. If the jaws are clamped on tissue when the supply of staples is depleted, the tissue may suffer unnecessary tissue trauma. Further, a laparoscopic stapler typically has knife which is intended to cut between rows of applied staples. If the staples are not present and the stapler is fired, the knife blade may cut tissue that is intended to be closed by the missing staples, clearly an undesirable result.